LAUSANNE, Switzerland -- The International Olympic Committee has empowered itself to award the 2024 and 2028 Summer Games simultaneously in September, pending an agreement between its own leadership and the Paris and Los Angeles bid committees.

Tuesday's unanimous vote put the two cities one step closer to hosting after frustrating droughts for France, which had mounted five previous Summer and Winter Games campaigns in the past 20 years, and the United States, which has seen two Summer Games bids rejected and one official candidacy fizzle since 2005.

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Why are Los Angeles and Paris the last two cities standing in an Olympic bid process that can be fraught with risk? Look no further than their respective mayors, Eric Garcetti and Anne Hidalgo, who have changed the game along the way.

Now the weight of negotiations will fall to the political and administrative leadership of Paris 2024 and LA2024, and specifically to the two mayors who would sign host city contracts -- Eric Garcetti of Los Angeles and Paris' Anne Hidalgo. The two already have a good rapport, chiefly from their work on international climate change issues.

They face a fairly compressed time frame to hammer out a deal before the IOC's meeting on Sept. 13 in Lima, Peru.

However, that process looked to be off to a promising start when Garcetti and Hidalgo walked onto the dais immediately after the vote to thank the room. The mayors then clasped and raised their hands with IOC president Thomas Bach. The mayors and bid leaders Casey Wasserman (LA2024) and Tony Estanguet (Paris 2024) also appeared at a joint news conference and posed for photos with Bach afterward.

"We're thrilled with the IOC's decision today, which is a major step forward in making LA's Olympic dream a reality" LA2024 said in a statement. "Today, two of the world's greatest cities, with outstanding but different proposals, stand ready to serve and advance the Olympic and Paralympic movements and their values.

"We look forward to working with the IOC and Paris in the weeks ahead to turn this golden opportunity into a golden future together."

Anne Hidalgo, the mayor of Paris, and Los Angeles Mayor Eric Garcetti must reach an agreement as to which city would host the 2024 Summer Games and which will host in 2028. Fabrice Coffrini/AFP/Getty Images

A potential agreement would determine which city would host first, begin to address issues related to financial guarantees for facilities and land use, and outline collaboration between organizing committees in operational expertise and promotions.

Paris 2024 has consistently taken a harder line, saying it would not consider waiting until 2028, while those stumping for LA2024 have indicated more flexibility in recent months. Garcetti has said he would push for some financial compensation, which likely would be channeled into youth sports, in return for deferring to Paris.

If an agreement is reached, the IOC would vote on whether to ratify it in Lima. If not, the IOC would choose between the two cities for 2024 only and leave the 2028 bidding process open.

Bach said an agreement would be made public when it is reached rather than waiting until the September meeting.

Garcetti said he had "full confidence" that the parties involved -- which include each country's national Olympic committee -- would come to terms, and likened Tuesday's outcome to a rare tie for an Olympic gold medal. Hidalgo pledged her complete "energy, will and creativity" to the process. Both adeptly circumvented questions about whether they would consent to waiting another four years to host the Games.

Talks will start at least informally on Tuesday night, according to Bach, who said he and the mayors planned to drink California Chardonnay and French Bordeaux wines with dinner.

The IOC's procedural decision in Lausanne represents a nod to what Bach called a "new political reality'' that is making it harder for bid cities to sell the massive project to their citizens, and an acknowledgment of two strong, pragmatic bids from recently spurned countries.

In the 2024 cycle alone, Hamburg, Rome and Budapest withdrew bids because of grassroots and political opposition, and the U.S. Olympic Committee switched its nominee after Boston's plans encountered stiff resistance.

Competition for the 2022 Winter Games also withered and came down to two cities, with the unlikely locale of Beijing prevailing over Almaty, Kazakhstan.

"Today, when people see that ... the entire establishment is united behind one project, then the people immediately have mistrust and conclude that something must be terribly wrong,'' Bach said.

The bidding process that worked to the IOC's advantage in the past "has become too expensive and too onerous,'' Bach added. "We have asking too much too soon from the candidate cities.''

Both Paris and Los Angeles tailored their bids to the set of IOC reforms called "Agenda 2020,'' which emphasized use of existing facilities, sustainability and a lasting legacy for the host city in contrast to the lingering debt and disillusion that have marked some Games in recent years.

The cities' presentations to the full IOC membership Tuesday morning took place behind closed doors at the IOC's request, and their relentlessly positive speeches and themes were released to reporters shortly afterward.

Newly elected French president Emmanuel Macron traveled to Lausanne for 24 hours of avid public and private lobbying on behalf of Paris 2024.

"I think that we are ready, that it's the right moment for the country, that our fellow citizens have been waiting for this bid and this win, to show the rest of the world what we're capable of doing,'' Macron told reporters.

The Paris and Los Angeles pitches amounted to semifinal victory laps after glowing reviews from the IOC's Evaluation Commission published last week. Should an agreement be reached before the Lima session, it's possible the bid committees would elect to forego or scale back the usual last-minute stage productions to cut costs.

The IOC's vote was the latest twist in a campaign that has played out in increments. Olympic distance swimming champion Janet Evans, a native of the Los Angeles area and LA2024 vice chair, said she was tired but "pleased and optimistic'' after the decision.

"The last freestyle lap of a 400 IM would be a good analogy,'' she said.

Several IOC members expressed concern about the big-picture risks and fine print attached to locking in a Summer Games 11 years in advance. Aside from practical questions about facilities and land use, the extra lead time represents another four years in which opposition could coalesce.

But in the end, there were all ayes and no nays in the raised-hands vote. That reflects the fact that many within the IOC want to end the recent, embarrassing trend of attrition.

Longtime IOC member Richard Pound is one of them. The dual allocation "buys us time to take a longer-term view of how we attract and encourage candidate cities,'' he told his colleagues during the session. As for this summer's 2024/2028 negotiations, Pound added, "This has to be a no-fail mission. If there's a failure, it's going to be viewed as a failure of the IOC.''

As Pound spoke to reporters after the meeting, Bach walked up to him and the two embraced.